Through the years, fork lift trucks have become an indispensable part of warehouse operations and plant inventory control. Their ability to maneuver in tight spaces and confined areas is legion. It is within these tight and difficult to maneuver areas that a vehicle operator will often find it necessary to maneuver the vehicle in both directions. Generally, the vehicle is configured, from a controls point of view, in a preferred mode of operation (e.g., forks leading versus tractor leading). Very often while facing the less preferred direction, the operator will still be working the controls and will continue to steer and operate the vehicle. It is at these times that the steering wheel will be inadvertently turned in a direction opposite to that intended by the operator.
The invention reflects the discovery, based on observing plant operations over many years, that even experienced vehicle drivers will often confuse the steering wheel direction when they face the less preferred direction of the vehicle. It is at these times that it would be useful to have a system that would automatically and/or manually reverse the steering wheel controls, such that the direction of steering wheel rotation is consistent with the direction of vehicle rotation, so that the vehicle driver can continue to move within the confined area with alacrity and dispatch.
The present invention has developed a system that determines or senses the direction of travel of the vehicle, and automatically and/or manually applies the appropriate steering controls to the vehicle. In other words, when a vehicle driver requests travel in the opposite to normal direction, and the vehicle begins to travel in that specified direction, the steering wheel will respond oppositely to the normal steering direction. Thus, a clockwise turn of the steering wheel that would normally turn the fork lift truck to the right, when facing the normal travel (fork leading) direction, will now direct the vehicle to the right when the vehicle is travelling opposite to the normal direction (i.e., the tractor leading direction), and vice versa.
The change of "steering sense" in accordance with this invention can be accomplished in several ways: (1) a velocity and direction sensor connected to the drive motor detects the direction of travel, and by means of feedback control is used automatically to orient the polarity of the steering motor relative to the direction of travel; (2) a reverse drive control lever mounted on the control panel of the fork lift truck generates a signal for directing a microprocessor controller to reverse the polarity of the steering motor; and (3) an accelerometer mounted upon the material handling vehicle senses the direction of movement of the vehicle, and sets the polarity of the steer motor accordingly.
The automatic reversing control of the present invention can also be manually actuated, over-ridden, or cancelled by a manually actuated control switch built into the control panel of the truck.